Christian warrior (8)
I believe the answer is:
crusader
'christian warrior' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for crusader that I've seen before include "Person engaged upon a cause" , "Advocate for a cause - rude scar (anag)" , "Campaigner -- rude scar (anag)" , "Vigorous campaigner" , "Champion" .)